Week 9 - Development of the CNS and Spinal Cord

Question 1

What are the 3 germ layers in an embryo?

Answer 1

ectoderm
mesoderm
endoderm

Question 2

What germ layer is neural tissue derived from?

Answer 2

neuroectoderm

Question 3

How is the neural tube formed?

Answer 3

process of NEURULATION

primitive streak goes through a process of neuralation that gives rise to both the brain and spinal cord

Question 4

Describe the process of neurulation

Answer 4

1. neuroectodermal tissue differentiates from ectoderm and thickens into the neural plate. the neural plate border separates the ectoderm from the neural plate
2. the neural plate bends dorsally forming neural folds as parallel ridges along the embryo.
3. the two neural plate borders join together and referred to as the neural crest
4. the neural fold meet at the midline to fuse forming the neural tube. fusion starts at the centre and moves both cranially and caudally. neural crest cells separate from the neural folds and differentiate to form most of the PNS
5. notochord degenerates only persisting as the nucleus pulposus of the invertebral discs. Other mesoderm cells differentiate into somites - the precursors of the axial skeleton and skeletal muscle.

Question 5

When does the process of neurulation take place?

Answer 5

around 3 weeks post fertilisation

Question 6

What are the 3 regions of CNS development of the early embryo?

Answer 6

prosencephalon (forebrain)
mesencephalon (midbrain)
rhombencephalon (hindbrain)

Question 7

As the embryo develops, what do the early embryonic structures develop into in the late embryo and in turn the adult brain?

Answer 7

prosencephalon -> telencephalon –> cerebrum
prosencephalon -> diencephalon –> diencephalon - thalamus, subthalmus, epithalamus and hypothalamus

mesencephalon -> mesencephalon –> midbrain

rhombencephalon -> metencephalon –> pons and cerebellum
rhombencephalon -> myelencephalon –> medulla oblongata

Question 8

What does the neural tube lumen become in each of the developing areas?

Answer 8

• telencephalon - lateral ventricles within the cerebrum
• diencephalon - 3rd ventricle within the diencephalon
• mesencephalon - cerebral aqueduct behind the midbrain
• metencephalon - 4th ventricle between pons and cerebellum
• myelencephalon - central canal for CSF

Question 9

What structures do the neural crest cells go on to become?

Answer 9

Cranial - cranial (parasympathetic and sensory) ganglia

Trunk - dorsal root ganglia and sympathetic ganglia

Vagal and Sacral Neural Crest - ENS (enteric nervous system) ganglia and parasympathetic ganglia

Meninges (mixed with mesoderm)